A motion picture produced in a 35 mm film format is intended to be exhibited in a conventional format cinema or in other smaller formats like home video and broadcast television. The display resolution required to maintain adequate display quality can be calculated based on the screen size, the theatre geometry, audience seating positions as well as the minimum visual acuity that needs to be maintained in order to deliver the required image quality. In a conventional cinema, a display resolution of around 2000 pixels across the width of the screen is considered adequate for delivery of satisfactory image quality. This resolution requirement is largely supported by the 35 mm film formats as well as by existing film production process chain from original photography, post-production, to film laboratory process. A similar display resolution requirement is also recommended for digital cinemas designed to replace conventional film-based cinemas.
In a large format cinematic venue, audiences expect a significantly superior visual experience to that which they perceive in a conventional cinema. Audiences in a large format cinema enjoys a field of view much larger than that from a conventional cinema. To maintain a superior visual experience in a large format cinema, the film production chain must deliver a spatial image resolution much higher than that for a conventional cinema. The current 15/70 film format production process chain adequately supports this higher spatial resolution requirement. However, when a motion picture originated for the 35 mm film format is to be exhibited in a large format cinema venue, the existing production system and process cannot deliver sufficient image quality. The present invention defines a method of digitally re-mastering a 35 mm motion picture with enhanced image resolution and quality as demanded by the large format cinematic experience.
The digital re-mastering process of the present invention is primarily (but not exclusively) used for the enhancement of image resolution of a motion image sequence originating with live action film photography. This process can be applied to the enhancement of computer generated animation or cell animation images that have been transferred to film. The digital re-mastering process can also be used to enhance the resolution and the quality of moving images captured using an optical imaging device or an electronic sensor device.
One aspect of the digital re-mastering concept of the present invention is that spatial resolution of each image frame in a live action motion picture sequence can be enhanced through temporal image processing. This is very different from the concept of film restoration in which “cleaning up” noise and “removing” artifacts are primary goals. There were many successful film restoration projects in the past two decades, and typical examples are Disney's Snow White and Seven Dwarves re-release and subsequent George Lucas' Star Wars trilogy re-releases. Most film restoration methods are designed to compensate for the loss of image quality caused by the deterioration of film conditions and to restore the characteristics of images close to the original form. Since the targeted re-release platform for a film restoration project is usually the same conventional cinema that the film was originally intended to be exhibited, or even smaller exhibition formats like home video and television, enhancing the spatial resolution of original imagery is not a major concern for film restoration.
The digital re-mastering process of the present invention should also be distinguished from existing methods for re-mastering an animated motion picture for large format releases, such as Disney's Fantasia 2000 and Beauty and Beast large format release production. In those efforts, image data was originally created in a digital form and was not corrupted by a film transfer process. As a result, the spatial resolution of image frames cannot be further enhanced through image processing methods unless those images are re-rendered in more detail. The method used in Fantasia 2000 and Beauty and Beast re-releases cannot enhance the image resolution of live action film photography.
The most straightforward method of displaying a 35 mm film originated motion picture in a large format cinema is to use a projection lens with a larger magnification to fill the entire screen. This method cannot deliver sufficient visual quality due to the fact that images on a 35 mm release print do not have sufficient spatial resolution. A better method is to digitally enlarge each frame of the motion picture using digital spatial interpolation methods and record the enlarged image data onto a large format film, like the 15/70 film format, for projection. The existing spatial interpolation methods do not improve spatial resolution and often soften images. Certain spatial high-pass filtering methods can be used to improve perceived image sharpness, but those methods also emphasize the noise in the images, like film grain. To reduce image noise, certain low-pass spatial filters can be applied, but those filters inevitably remove image details. Therefore, conventional spatial processing methods cannot satisfy conflicting demands for noise reduction and maintaining image sharpness.